To your 4 methods
1) Mass sacrifice well this works per the rules pretty clearly, and easily if you can catch the 5 people. Worse, you can even sacrifice WVC, ghouls, or like as far as I can tell. And you can do similar by mass inflicting consequences.
2) I don't think 10 rabbits counts as a person, if they did no one would sacrifice anyone when they can buy stuff at the pet store. At best with sufficient rolls I would let declarations like ANIMAL SACRIFICE, LOTS OF ANIMAL SACRIFICE, ENDLESS BLOOD, BlOOD MAGIC, but those are really just declarations.
3) 50 declarations is hard. I know someone here made a system to adjudicate the difficulty and time requirements of declarations. Just use that, or similar.
4) It technically works, but at 4 scenes a game, your wizard comes back 25 games later. ... Its really not going to happen.
So most of these ways don't really work. Now how do you balance against big rituals? Well what can you even do with a 100 shift ritual that a 40ish shift can't? (Lore +5 Moderate +5 Mild + Change) I suppose you can help punch through wards and such, or make it area of effect to zot a city block, but really? A lot of baddies won't have wards. (No threshold). An aspect pile can be done just as well with 10 20ish shift rituals. What is seriously going to mess with a 30 strength ward? Even a patently inane healing spell would top out before 40...
So whats the big problem? Its just Thaumaturgy doing what it does. If the PC's are really dedicated and have a symbolic link they can asplode the targets brain. If they really want they can aspect pile. So what is the problem going from 40ish to 100ish?